1. Field of the Invention
The present invention relates to a device of automatically compensating for the brightness of a screen of a cathode ray tube (CRT) and a method thereof. More particularly, the method is used for automatically compensating for the brightness of a screen by computing an added value of a factor for decreasing the brightness of CRT and outputting a control signal for adjusting the brightness with the computed value.
2. Discussion of Related Art
In general, among peripheral devices for processing data generated in main system of a personal computer (PC), a display monitor is a device used for displaying the data as images on a screen. The display monitor is a device for displaying data generated in the main body of PC at the fastest speed and most conveniently. The monitor is connected generally with the main device as a peripheral device among those data processing systems.
The general display monitor will be described below with reference to the attached drawings.
FIG. 1 is a block diagram illustrating an inner circuit of a general monitor. As shown in the drawing, PC 100 includes CPU 110 for receiving a key board signal input by a user, processing and generating data according to the result of the process; and a video card 120 for receiving data output from CPU 110 to process into R. G. B. video signals, and outputting the processed R. G. B. signals and horizontal and vertical synchronization signals H-SYNC and V-SYNC for synchronizing the R. G. B. video signals.
A monitor which receives the R. G. B. video signals and the horizontal and vertical synchronization signals H-SYNC and V-SYNC output from the video card 120 in the PC 100, includes a micro computer 210 for receiving the horizontal and vertical synchronization signals H-SYNC and V-SYNC; a control button unit 220 for generating and outputting a screen control signal for controlling a monitor screen; a horizontal and vertical output circuit unit 230 for receiving a monitor screen control signal and a reference oscillation signal output from the micro computer 210 and synchronizing a raster; a video circuit 240 for receiving and displaying the R. G. B. video signals output from the video card 120; and a power circuit 250 for supplying power voltage to the micro computer 210, the horizontal and vertical output circuit 230, and the R. G. B. video signal processing unit 240.
Each block in the thus-structured monitor 200 will be described in detail.
The micro computer 210 receives the horizontal and vertical synchronization signals H-SYNC and V-SYNC from the video card 120. The micro computer 210 has the various monitor screen control data.
If the control button unit 220 applies a monitor screen control signal to the micro computer 210, the micro computer 210 outputs an image control signal for controlling image displayed on the screen according to the screen control signal. The control button unit 220 outputs the horizontal and vertical position control signals and the horizontal and vertical size control signals. The micro computer 210 receiving the monitor screen control signal outputs an image control signal and a reference oscillation signal.
A horizontal and vertical oscillation signal processor 230-1 receiving the image control signal and the reference oscillation signal from the micro computer 210 controls the switching speed of an on/off operation of a saw tooth wave generation circuit 230 according to the horizontal and vertical synchronization signal H-SYNC and V-SYNC applied from the video card 110. A vertical pulse drive circuit 230-2 receives a vertical pulse from the horizontal and vertical oscillation signal processor 230-1. In general, for the vertical pulse drive circuit 230-2, there are used a single stage vertical amplifying type and an emitter follower type for receiving input through a base and outputting output through an emitter. Therefore, the circuit improves its straightness rather than gains.
The vertical output circuit 230-3 receiving the current signal from the vertical drive circuit 230-2 generates the saw tooth wave current conformed with the vertical synchronization pulse flowing through V-DY 230-4, and thus determines a vertical scanning period. In addition, a horizontal drive circuit 230-5 receives a horizontal oscillation signal output from the horizontal and vertical oscillation signal processor 230-1. The horizontal drive circuit 230-5 supplies current sufficient for turning on/off the horizontal output circuit 230-6. To be used for the horizontal drive circuit 230-6, there are two methods: an in-phase type in which when drive terminal is at ON state, its output terminal is at ON state; and an anti-phase type in which when the drive terminal is at ON state, its output terminal is at OFF state, the method being widely used currently.
The horizontal output circuit 230-6 which receives the current from the horizontal drive circuit 230-5 generates the saw tooth wave current to H-DY 230-7. The horizontal scanning period is determined by this saw tooth wave current.
A fly-back line collector is used for supplying the stable DC voltage to an anode terminal 2404-1 of CRT 240-4 through a flyback transformer (FBT) 230-9. With a small collector pulse, a high voltage is generated and applied to the anode terminal 240-2-1 of CRT 240-3 by using higher harmonics according to a leakage inductance and a distributed capacity.
There follows a procedure of displaying the R. G. B. video signals to CRT 240-3 in the video signal processor 240 receiving high voltage through the anode terminal 240-4-1.
An OSD unit 240-1 receiving OSD gain signal generated according to the screen control of the micro computer 210 generates and outputs OSD gain signal. A video pre-amplifier 240-2 receiving the OSD gain signal and the R. G. B. video signals from the video card 120 amplifies the low R. G. B. signals by a low-voltage amplifier to thereby maintain a predetermined level. For example, a signal below 1 V.sub.pp is amplified to a signal of 4 to 6 V.sub.pp. The amplified signal is re-amplified to 40 to 60 V.sub.pp through a video main amplifier 240-3, and is used for supplying energy to each pixel. The video signals amplified in the video main amplifier 240-3 is applied to a cathode of CRT 240-3 to display the R. G. B. video signals on the monitor screen.
A power circuit 250 for supplying a driving voltage required for displaying the video signals receives alternating current (AC) through an input port 250-1. A degaussing coil 250-2 receiving AC recovers a chromaticity on the screen whose saturation is decreased because of a spread caused from an earth magnetic field or external condition, into an original state. For this operation, if AC is applied for two to eight seconds to the degaussing coil 250-2, the magnetic field formed on the shadow mask in the monitor gets diffused, and thus the spread of a color is retrieved into the original state. The AC is rectified through the AC rectifier 250-3 and output to a switching transformer 250-4. The switching transformer 250-4 performs a switching operation, and supplies various operating voltages required for the monitor 200 through a voltage output terminal 250-5.
Here, if the vertical synchronization signal V-SYNC is not applied from the video card 120, the micro computer 210 cuts off the deflection voltage by applying a suspend-mode signal to the voltage regulator 250-6. A pulse-width modulation unit (PWM) 250-7 performs an on/off operation of the switching device with a curved-wave pulse, and the variation of the pulse width increases/decreases the conduction time, stabalizing the output voltage. If the micro computer 210 cannot detect the horizontal and vertical synchronization signals H-SYNC and V-SYNC, the micro computer 21 applies a power off mode signal to PWM unit 250-7. The PWM unit 250-7 becomes low level, and therefore cuts off the voltage applied to the monitor 200. Accordingly, it saves power consumption in the monitor.
With reference to the attached drawings, there will be described below the structure of CRT 240-4 which displays the R. G. B. video signals used in the conventional display monitor or television.
In FIG. 2, there are illustrated a base 240-4a and an outer lead 240-4b each for receiving the R. G. B. video signals and heating current; a magnet assembly 240-4c and an electronic gun 240-4d for generating electronic beam 8 according to the video signals, controlling an amount and speed of the electronic beam 8 and serving as a lens; horizontal and vertical deflection coils 240-4e and 240-4f for deflecting the electronic beam 8 in every direction; a shadow mask 240-4g dot or stripe-structured on a thin steel plate to make contact with the fluorescent chromatic material in correspondence with the electronic beam 8; a screen 240-4h on which the fluorescent material is coated to emit light when the electronic beam 8 passing through the shadow mask 240-4g makes contact with it; a getter 240-4j for gathering contaminants and sticking them onto a wall of a funnel 240-4i, namely, a glass tube in order to increase vacuum degree in CRT 240-4; an anode junction point 240-4-1 for receiving high voltage from FBT 230-9 (refer to FIG. 1); a glass panel 240-4k; a magnetic shield 240-4l; and a tension band 240-4m.
The thus-structured general CRT operates as follows.
The electronic gun 240-4d generates great or small beam 8 according to the intensity of the R. G. B. video signals from PC 100 (see FIG. 1). This cathode electronic beam 8 proceeds toward the plate by being led by the high anode voltage applied to an anode grid (or plate, not shown). When, the accelerated electronic beam 8 passes through the plate and hit the screen 240-4h coated with fluorescent material on the surface flourescent material on the surface of CRT 230-4, the energy of the electronic beam 8 is emitted in the form of light. The light signal is scanned in every direction of CRT 240-4 by the horizontal and vertical deflection coils 240-4e and 240-4f, thus displaying the R. G. B. video signals.
There will be described the variation of brightness of the thus-structured conventional CRT 240-4 with time with reference to the attached drawings.
As illustrated in FIG. 3, Y axis of a graph represents the brightness of the screen, and X axis represents the used time of the monitor in the unit of 1000 hours, namely, 1K hour. When using the monitor firstly in this graph, the brightness of the screen is lowered from 100% to 80% via 8K hours, namely, 8000 hours (The test should be performed in the same condition). With a lapse of the used time of the monitor, a gradual decrease of the brightness is because the amount of the electronic beam generated in the electronic gun 240-4e is decreased, and also because when the fluorescent material coated on the screen 240-4h emits light, it is ignited and thus its light emitting efficiency is decreased.
Though the characteristics of the components used for the display monitor and television are improved to thereby extend the life time, its light emitting efficiency of the fluorescent material in CRT is however decreased, accordingly decreasing the brightness of the screen below the regulated value only in one or two hours.